kernel hangs at boot on dual G5

[Lucio Crusca <lcml@pixel.it>]

Hello *,

I'm trying to install Sarge on a dual G5 from the official DVD iso, but the
kernel hangs on boot with the following messages:

... ok
opening diplay /pci@0,f0000000/ATY,ChockStoneParent@10/ATY,ChockStone_B@1...
ok
opening OF device tree... done
starting CPU /cpus/PowerPc,g5...failed: 00000000
Initalizing fake screen: ATY,ChockStone_a
Calling quiesce ...
returning 0x01400000 from prom_init

Invalid memory access at   %SRR0: 00000000.01403v88   %SRR1:
10000000.00083030

Apple PowerMac 7,3 5.2.4f1 BootROM built on 03/25/05 at 16:41:34

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My G5 has 4GB ram, I've already tried mem=512m but the result is just the
same. Any clue?